Switching apparatus



Dec. 13, 1955 F. KESSELRING 2,727,114

SWITCHING APPARATUS Filed June 15, 1955' United States Patent C) SWITCHING APPARATUS Fritz Kesselring, Zollikon, Zurich, Switzerland, assignor to FKG Fritz Kesselring Geratebau A. G., Bachtobei- Weinfelden, Thurgau, Switzerland, a corporation of Switzerland Application June 15, 1953, Serial No. 361,777

Claims. (Cl. 200166) My invention relates to contact switching devices and is more particularly directed to the design and construction of apparatus to eliminate bouncing of the movable contact during the closing operation and to prevent oscillation of the moving contact during the opening operation.

The switching apparatus to which my invention is directed is of the type having a substantially massless armature which is normally biased to the disengaged position. On the occurrence of a sufficiently strong electromagnetic force to overcome the biasing means, the armature is moved to its closed position to thereby engage the stationary contacts. This type of switching apparatus is primarily used in electromagnetic rectifiers.

The switching apparatus used in electromagnetic rectifiers, which have substantially massless armatures traveling at finite speed during the closing operation are susceptible to shocks due to the impact resulting from the closing force. Thus, unnecessary bouncing, mechanical wear, burning of the contacts and frequently the freezing or welding of the contact surfaces may result from improper operation.

In many applications of electromagnetic switch, especially as above pointed out, the apparatus will have to perform many billions of switching operations throughout the year. Hence, it is essential that the switch operate without shock or bounce.

As is wellknown in the mechanical arts, the impact of a first body on a second may result in a transformation of the kinetic energy of one body into potential energy in that body. Hence, the release of the potential energy may result in the bouncing of the first body oif the sec ond body following an impact. That is, if a sphere is dropped on a flat surface, it will be slightly flattened at the impact thereby storing potential energy in the sphere. Following the release of the potential energy, the sphere again acquires kinetic energy and will rebound back to a height which is slightly smaller than the original distance of the fall. This bouncing will continue until the original energy imparted to the sphere is dissipated by friction or other means.

In my novel invention, I provide resilient stationary contacts to which a portion of the movable contact kinetic energy can be imparted to thereby more readily dissipate the energy to prevent rebounding of the armature.

I have found that by properly coordinating the characteristics of the resilient stationary contacts with the closing force and path of movement of the movable contact, I am able to obtain switching operation without bouncing.

When there is a force of between 50 and 100 kg. acting on a movable armature which moves at approximately 0.5 meter per second, no bounce will occur if the path of movement of the movable contact is not more than a few microns (,u). However, this severe limitation is not practical in an electromagnetic switch and is overcome by my invention by designing the dampening spring with a, spring constant which bears a relationship to the vertical closing force, length of movement of the armature and dampening force of the system.

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For a particular magnetic pole F, the vertical component which urges the movable contact toward engagement will be Fv, and the length of the path of movement of the armature is designated by an X.

The ratio of the rebound height hi to the original heighth of the spring is equal to the of the dampening coefiicient K, thus The dampening force is designated as (K). By providing a system wherein the mass of the dampening springs is considerably less than the mass of the armature or movable contact, i can provide a completely dampened or anti-bounce system by designing the spring constant to fulfill the following equation:

The dampening force (K) depends only to a small degree upon the type of spring being used and for values up to Z :0.4 /(K), K will be approximately equal to F with a dampening spring mass which is equal to or less the mass of the moving contact. The spring system which is designed with a spring constant according to the above equation will sufficiently absorb the kinetic energy of the moving contact when it is moved into engaged position and carry out the operation without bouncing.

Additional means may be provided whereby stronger dampening springs may be used and still avoid the possibility of the bouncing of the movable contact. In this arrangement, a suspended mass is positioned in the plane of the dampening springs so that engagement between the moving contact and the bumper body will occur simultaneously with the engaged of the movable contact and the dampening springs. In this arrangement, the combined mass of the dampening springs and bumper bodies are equal to the mass of the moving contact. Thus, on the simultaneous engagement of the movable contact with the dampened spring and bumper bodies, the kinetic energy of the movable contact will be imparted to the bumper bodies and the impact of these bodies will move them in the same direction as the path of movement of the movable contact.

Since a major portion of the energy has been imparted to the bumper bodies, the movable contact and dampening springs will remain in engagement and no bouncing therebetween will occur.

Since the design of the electromagnetic switching device provides for current carrying dampening springs, this latter arrangement incorporating bumper bodies will enable a more rigid design of the dampening springs of substantially greater cross-sectional area thereby reducing the effective resistance to the current passing therethrough.

Accordingly, a primary object of my invention is to provide a novel electromagnetic switch wherein the stationary contacts are comprised of a set of resilient springs which may deflect when engaged by the movable contact.

Still another object of my invention is to provide a novel arrangement in which the stationary contacts will absorb a substantial amount of the kinetic energy of the moving contact.

A still further object of my invention is to provide an electromagnetic switch in which the engagement between the movable contact and the stationary contacts following an impact blow permits the transformation of kinetic energy from the moving member to the semi-stationary member.

Still another object of my invention is the provision of an anti-bouncing means whereby the kinetic energy of the moving body is transformed to a second body to prevent chattering or bouncing of the cooperating surfaces.

A still further object of my invention is to provide an electromagnetic switch having a resiliently mounted mass in the plane of the stationary contacts whereby a billiard ball effect can be achieved upon the impact engagement of the movable contacts with the stationary contacts.

Still another object of my invention is to provide an arrangement in which the movable contacts will simultaneously engage dampening springs comprising the stationary contacts and bumper bodies which are designed, constructed and arranged to prevent bouncing of the cooperating contacts.

A still further object of my invention is the provision of an electromagnetic switching device in which a resiliently mounted body having a mass slightly less than the mass of the moving contact will extract a major portion of the kinetic energy from the moving contact to thereby permit impact engagement between the moving body and the dampening springs comprising the stationary contacts 1 without bouncing.

A still further object of my invention is the provision of means to prevent the oscillation of the moving contact following contact separation.

These and other objects of my invention will be apparent from the following description when taken in connection with the drawings in which:

Figure l is a side cross-sectional view of one embodiment of my novel electromagnetic switch having a leaf spring arrangement to prevent the oscillation of the moving body upon contact separation and a leaf spring arrangement to prevent bouncing of the contact upon engagement.

Fig. 2 is a top view of the electromagnetic switch of Figure 1. The arrows 1--1 of Figure 2 indicate the cross-sectional view seen in Figure 1.

Figure 3 is another embodiment of my novel dampening and anti-oscillating electromagnetic switch which incorporates resiliently mounted masses to aid in the dampening operation. Figure 3 provides a leaf spring arrangement for the stationary contacts the same as in Figure 1 but incorporates a slidably mounted movable contact member to prevent oscillation following the opening operation and adds bumper bodies to aid in the dampening during the closing operation.

Figure 4 illustrates another embodiment of my invention incorporating the leaf spring arrangement to prevent oscillation during opening as seen in Figure l and substitutes flat springs for the stationary contacts.

Referring now to Figures 1 and 2, the terminal conducting members 12 and 13 are separated by the insulating member 29 which is securely secured thereto by means of screws 34 and 35. A plurality of leaf springs 10 and 11 are permanently secured to the terminal members 12 and 13 by means of the screws 36 and 37. Screws 36 and 37 also secure the insulating members 8 and 9 which support the anti-oscillation leaf springs 6 and 7 and the armature-movable contact biasing spring 5.

U-shaped magnetic yokes 38 and 39 have the magnetic poles 16-18 and 1719 surrounding the terminal conducting members 12 and 13.

The movable switching element 1 is comprised of a centrally disposed conducting portion 2 which is made of copper or any other good electrical conducting material and magnetic material at its extremities 3 and 4. The centrally disposed portion 2 represents the moving contact and the external magnetic portions 3 and 4 function as the armature of the switching device. The flat spring 5 biases the armature-moving contact 1 to the neutral disengaged position, as seen in Figure l.

The plurality of leaf springs 10 and 11 provide dampening for the system due to the friction between the spring leaves and also serve as current conductors. As noted, the dampening springs 10 and 1 1 are electrically con,

nected to the terminal conductors 12 and 13 by pressure e a emen c eated by he screws 36 nd 37.

The dampening springs 10 and 11 are preferably made of a good electrical conducting material such as silver aluminum or an alloy of proper beryllium. However, it will be noted that the springs 10 and 11 may also be made of steel and the electrical conducting path may be provided by silver plating the steel springs.

The extensions 8a and 9a of the insulating supporting members 8 and 9 serve as stop gages and determine the neutral fixed position of the dampening springs 10 and 11, as seen in Figure l. A material which has a higher resistance to abrasion than the springs 10 and 11 may be disposed between the layers of the dampening springs 10 and 11 at the area indicated by Na and 11a.

The terminal conducting members 12 and 13 are provided with extensions 14 and 15, the function of which will hereinafter be described.

The top surfaces of the terminal extensions 14 and 15 are disposed below the surfaces of the leaf springs a d The operation of the electromagnetic switch is as follows: On the occurrence of a closing force which is greater than the biasing force of the spring 5, the switching element 1 comprising the moving contact 2 and the armature 3 and 4 will be moved downwardly. The switching element 1 will then impinge upon the two uppermost leaf springs 10 and 11. At the moment of impact of the switching element 1 on the uppermost leaf springs 10 and 11, a current conducting path will be provided from the terminal conductor 12 through the leaf springs 10 to the movable contact 2, the leaf springs 11 and out through the terminal conductor 13. However, at this moment, the switching element 1 will continue to move downwardly until it has dissipated all of ts k e c ne y- At the end of the movement of the switching element 1, the moving contact 2 will come into engagement with the extensions 14 and 15 of the terminal conductors 12 and 13. At this point, current will now flow through the low resistance parallel path comprised of the terminal conductor 12, its extension 14, movable contact 2 of the switching element 1 terminal 15 to the terminal conductor 13.

As illustrated in Figure 1, a top surface of the uppermost leaf springs 10 and 11 are in a plane above the top surface of the extension stationary contacts 14 and 15. In a preferred arrangement, the distance between the top surface of the uppermost leaf springs 10 and 11 above the top surface of the extension stationary contacts 14 and 15 is between /3 or A; of the total of distance traveled by the switching element 1.

It will be noted that since the dampening springs 10 and 11 serve as conducting members prior to the engagement of the movable contact 2 with the stationary contacts 14 and 15, it is desirable to construct the arrangement with a minimum amount of inductance. This is achieved by having the leaf springs 10 and 11 lie fiat on the terminal conductors 12 and 13 and having them permanently secured thereto by means of the fastening screws 36 and 37.

The means spring constant C of the dampening leaf spring arrangement 10 and 1.1 is chosen to fulfill the relationship Thus, for example, where the vertical closing force Fv is 0.5 kg. per leaf spring and the path of movement X of the switching element 1 is 0.02 cm. and for a copper material of the leaf springs 10 and 11 having a dampening coefficient (K approximately equal to 0.1, the mean spring constant C of less than 500 kg./cm. is obtained. Thus, the leaf springs 10 and 11 are properly dampened to prevent bouncing off the switching element 1 when it impinges on the leaf springs due to a closing force.

For the magnitudes above set forth, a triangular copper leaf spring having a width of 1 cm., a free length of 2 cm. and a thickness of 1.9 cm. will have a spring constant C of approximately 500 kg./cm. thereby satisfying the above equation and insuring that the electromagnetic switch will operate without bouncing.

When the closing force on the switching element 1 is removed, the flat biasing spring 5 will urge same toward its neutral position indicated in Figure 1. During this upward movement, the kinetic energy of the switching element 1 will be imparted to the plurality of leaf springs 6 and 7 to thereby prevent oscillation of the unit during the opening operation.

In Figure 3, I have shown an improved arrangement of my invention whereby the kinetic energy of the switching element 1 can be imparted to resiliently mounted masses 20 and 21. In this arrangement, the masses or bumper bodies 20 and 21 are mounted by separate springs 22 and 23 in the plane of the uppermost leaf spring 10 and 11. That is, the upper surface of the independently mounted bumper bodies 21 and 22 are flush with the upper surface of the dampened springs 10 and 11.

In the embodiment of Figure 3, the combined mass of the bumper bodies 20, 21, their supporting springs 22, 23 and the dampening springs 10 and 11 are equal to the mass of the switching element 1. Since the supporting springs 22 and 23 and the dampening springs 10 and 11 are extremely light, each of the bumper bodies and 21 is equal to approximately /2 of the mass of the switching element 1.

Flexible dampening plates 24 and are provided below the surface of the masses 20 and 21 and are preferably made of rubber or plastic in the form of stacked plates.

The mass supporting springs 22, 23 and bumper bodies 20, 21 have a natural frequency which is equal to the frequency of the source which is being rectified or equal to the number of opening and closing operations that the switch must go through in a predetermined period of time such as a second. Thus, when the switching element 1 is attracted to its engaged position, its impact with these last mentioned units 20 and 21 will drive these latter members toward the dampening plates 24 and 25, making the natural frequency of the combination supporting springs 22 and 23 and the bumper bodies 20 and 21 equal to the frequency of operation of the switching device. The bumper bodies 20 and 21 will return to their neutral position when the force on the switching element 1 is removed and its biasing spring 5 moves it to its disengaged position.

The operation of the electromagnetic switching device is as follows: When a closing force is exerted on the switching element 1 and is sufficient to overcome the biasing force of the spring 5, the switching element will be moved downwardly toward its engaged position, it will simultaneously impact on the uppermost leaf springs 10 and 11 and the mass units 20 and 21. At the moment of impact, a major portion of the kinetic energy of the switching element 1 will be transferred to the masses 20 and 21. At this instant, the bumper bodies 20 and 21 will be moved downwardly due to the kinetic energy imparted thereto and will engage the dampening plates 24 and 25.

It will be noted that a small portion of the kinetic energy will also be imparted to the dampening leaf springs 10 and 11 and hence, these latter units will also move downwardly a small distance while the switching element 1 remains in engagement therewith.

As heretofore noted, complete dampening operation without bouncing of the cooperating contacts can be accomplished by having the spring constant of the dampening springs 10 and 11 satisfy the equation heretofore developed.

However, in the embodiment of Figure 3, it will be noted that the distance travelled by the switching element 1 is considerably reduced since a major portion of its kinetic energy is transferred to the resiliently mounted masses 20 and 21 upon engagement therewith. Hence, a considerably larger closing force Fv with a substantially larger spring constant can be used with this system. Furthermore, the dampening springs 10 and 11 may therefore be larger in cross-sectional area hence presenting a small omhic resistance to the current flow. Thus, if it is assumed that the path of movement of the switching element 1 of Figure 3 is only /5 of the path of movement of Figure 1 and the vertical component of the closing force Fv is twice as large, then it is possible to obtain a spring constant for the dampening springs 10 and 11 which is ten times larger than the spring constant system used in Figure 1. That is, the spring constant C of dampening springs 10 and 11 for the arrangement of Figure 3 will be slightly less than 500 kg./cm.

In the arrangement of Figure 3, I have used the same numerals as in Figure l to denote similar parts.

On the engagement of the switching element 1 with the top surface of the leaf springs 10 and 11, a current path will be provided from the terminal conductor 12 through leaf spring 10, conducting portion 2 of the switching element 1 to the leaf spring 11 and thence to the terminal conductor 13.

In the preferred embodiment, as illustrated in Figure 3, I have shown the uppermost portion resiliently mounted bumper bodies 29 and 21 flush with the upper surfaces of the dampening springs 10 and 11. However, in some applications, it may be advantageous to allow the upper surface of the masses 20 and 21 to protrude over the leaf spring arrangement 10 and 11 by a small fraction and the moving distance, for example, A5 of the distance to he travelled by the switching element 1.

Since the supporting springs 22 and 23 for the masses 20 and 21 are not required to be current conductors, it may be advantageous to electrically insulate these units from the dampening springs 10 and 11.

In the arrangement of Figure 3, I have shown another modification which will prevent the oscillation of the switching element 1 following the opening operation. In this arrangement, the leaf springs 6 and 7 of Figure l are replaced by the stop gage 26 which is slidably mounted in the extension 27 which is maintained by the screw 36 to the insulating member 8. A flat spring 28 also secured to the extension 27 biases the slidably mounted stop gage 26 downwardly. When the switching element 1 is in the neutral position indicated in Figure 3 and when the switching element is in the closed or engaged position, the slidable or stop gage 26 is in the position indicated. When the closing force on the switching element 1 is removed, its biasing spring 5 will urge it upwardly toward its neutral position. Upon engagement with the stop gage 26 which is substantially the same mass as the moving element 1, the kinetic energy of this latter unit will be imparted to the stop gage thereby driving same upwardly. Since this arrangement provides a relatively simple and easy means to extract a major portion of the kinetic energy from the moving element, it will not have to dissipate ites energy by wind-losses and friction through oscillation following the opening operation.

The flat spring 28 which biases the slidably mounted stop gage 26 downwardly will urge same to its neutral position, as indicated in Figure 3, when the switching element 1 comes to rest.

In the illustrated arrangement of Figure 3, I have shown both the initial and final conducting path following the opening operation as showing the leaf springs 10 and 11. However, it will be apparent to those skilled in the art that the embodiment of Figure 3 may be adapted with terminal extensions similar to 14 and 15 of Figure 1 wherein the leaf springs 10 and 11 initially carry the load current and thereafter the current flows through the parallsl path of the t rminal e sions 1 and 15- In Figure 4, I have shown another embodiment of my invention which utilizes the leaf spring arrangement 6 and 7 described and illustrated in connection with Figure 1 to prevent the oscillation for the switching element 1 following an opening operation.

However, the dampening of the switch is provided with an arrangement which differs from that set forth in Figures l and 3. In this arrangement, flat springs 32 and 33 are secured to the terminal conducting members by means of the screws 36 and 37 which also secure the insulating supports 8 and 9 thereto. The flat springs 32 and 33 are biased upwardly, as indicated in the figure, and are so designed that when increased bending downwardly the contact surface between springs 32 and 33 and the terminal conductors 12 and 13 will be continually increased until the springs lie fiat on the surface of the conductors 12 and 13.

In the preferred arrangement, the kinetic energy of the switching element 1 will be dissipated by the friction created between the cooperating surfaces of the flat springs 32 and 33 when they are urged downwardly into engagement with the terminal conductors 12 and 13 to thereby provide dampening or anti-bouncing.

In the event that the compact design of the switch structure does not provide sufiicient frictional losses between the cooperating surfaces of the springs 32 and 33 and the terminal conductors 12 and 13, the springs 32 and 33 may be designed as leaf sprin s in order to absorb a portion of the kinetic energy from the switching element 1.

The design set forth in Figure 4 has the particular advantage of providing an electrical decreasing resistance path as the switch element is brought from its initial closed position to its final closed position. That is, with the springs 32 and 33 lying fiat on the top surfaces of the terminal conductors 12 and 13, a minimum resistance will be provided for the current path comprising a terminal conductor 12, the spring 32, the conducting element 2 of the switching element 1, the spring 33 and terminal conductor 13. it will be noted that the springs 32 and 33 may be designed as fiat springs or curved springs since the stress therein remains consant.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordin ly, I prefer to be bound not by the specific disclosure herein but only by the appending claims.

I claim:

1. A switching device comprising a switching element, a pair of stationary contacts and a pair of conducting dampening leaf springs; said switching element comprising a conducting portion and a magnetic portion; said stationary contacts and said pair of conducting dampening leaf springs each being spaced a distance less than the width of said conducting portion of said switching element; said switching element biased away from said dampening leaf springs and said stationary contacts; said magnetic portion operatively connected as an armature to move said switching element toward said leaf springs and said stationary contacts when said magnetic portion is sufiiciently energized; said switching element initially engaging said leaf springs before engagement with said stationary contacts; said switching element imparting its kinetic energy to said leaf springs to prevent bouncing thereof, said initial engagement between said switching element and said leaf spring completing a first electrical circuit through said leaf springs and said switching element; a second electrical circuit completed when said switching element engages said stationary contacts; said first electrical circuit being in parallel with said second electrical circuit.

A sw hi device ompris n a. switc in e ement, a pair of stationary contacts and a pair of conducting dampening leaf springs; said switching element comprising a conducting portion and a magnetic portion; said stationary contacts and said pair of conducting dampening leaf springs each being spaced a distance less than the width of said conducting portion of said switching ele ment; said switching element biased away from said dampening leaf springs and said stationary contacts; said magnetic portion operatively connected as an armature to move said switching element toward said leaf springs and said stationary contacts when said magnetic portion is sufficiently energized; said switching element initially engaging said leaf springs before engagement with said stationary contacts; said switching element imparting its kinetic energy to said leaf springs to prevent bouncing thereof; said initial engagement between said switching element and said leaf spring completing a first electrical circuit through said leaf springs and said switching element; a second electrical circuit completed when said switching element engages said stationary contacts; said first electrical circuit being in parallel with said second electrical circuit; a leaf spring arrangement to prevent oscillation of said switching element following opening operation.

3. In a switching device comprising a switching element and a pair of leaf springs; biasing means to bias said switching element away from said leaf springs; said pair of leaf springs spaced from each other a distance which is less than the width of said switching element; said switching element bridging said space of said leaf springs when moved to engaged position; said switching element imparting kinetic energy to said leaf springs; mass units resiliently and independently mounted and positioned in the plane of said leaf springs; said mass units being positioned from each other a distance which is less than the width of said switching element; said switching element imparting a major portion of its kinetic energy to said mass units when said switch is moved to its engaged position; said mass units having a natural frequency equal to the frequency of operation of said switching device; dampening plates to absorb a portion of the kinetic energy imparted to said mass units, said pair of leaf springs being conducting members and completing an electrical circuit through said switching element when said switching element is moved to engaged position.

4. A switching device comprising a switching element, a pair of stationary contacts and a pair of conducting dampening leaf springs; said switching element comprising a conducting portion and a magnetic portion; said stationary contacts and said pair of conducting dampening leaf springs each being spaced a distance less than the width of said conducting portion of said switching element; said switching element biased away from said dampening leaf spring and said stationary contacts; said magnetic portion operatively connected as an armature to move said switching element toward said leaf springs and said stationary contacts when said magnetic portion is sufficiently energized; said switching element initially engaging said leaf springs before engagement with said stationary contacts; said switching element imparting its kinetic energy to said leaf springs to prevent bouncing thereof; said initial engagement between said switching element and said leaf spring completing a first electrical circuit through said leaf springs and said switching element; at second electrical circuit completed when said switching element engages said stationary contacts; said first electrical circuit being in parallel with said second electrical circuit; a stop gage slidably mounted in the plane of movement of said switching element; said stop gage absorbing a major portion of the kinetic energy of said switching element following an opening operation.

5. In a switching device comprising a switching element; af sp n s and a top sa s switching m n n a ing said leaf springs during the closing operation and engaging said stop gage during the opening operation; said leaf springs absorbing kinetic energy from said switching element during the closing operation; said stop gage absorbing kinetic energy from said switching element during the opening operation; said stop gage preventing oscillation of said switching element during the opening operation; two bumper bodies resiliently mounted in the plane of said leaf springs; each of said bumper bodies having half the mass of said switching element; said switching element engaging said bumper bodies during the closing operation; said bumper bodies absorbing a major portion of the kinetic energy of said switching element.

References Cited in the file of this patent UNITED STATES PATENTS Millermaster Mar. 17,1931 Lederer Sept. 27, 1932 Matson Apr. 10, 1934 Agnew Oct. 17, 1939 Little Dec. 9, 1941 Pelletier Oct. 9,1951 

